1. Field of the Invention
This invention relates to the polymerization of olefins and more particularly relates to catalyst compositions useful for polymerizing ethylene, alone or together with one or more comonomers, to semi-crystalline resins.
2. Description of the Prior Art
It is known that catalysts of the type variously described as coordination, Ziegler, Ziegler-type, or Ziegler-Natta catalysts are useful for the polymerization of olefins under moderate conditions of temperature and pressure. It is also known that (1) the properties of the polymers obtainable by the use of such catalysts, as well as the relative economies of the processes used to prepare the polymers, vary with many factors, including the choice of the particular monomers, catalyst components, polymerization adjuvants, and other polymerization conditions employed, (2) gas-phase polymerization processes offer economic advantages over slurry and solution processes, and (3) supported catalysts are particularly desirable because of their utility in gas-phase, slurry, and solution polymerization processes.
British Pat. No. 1,489,410 (Monsanto) teaches polymerization processes, at least some of which are commercially attractive because of their use of supported Ziegler catalysts having a vanadium component and other factors, most notably their ability to be conducted by gas-phase, slurry, or solution techniques. However, attempts to make Monsanto's vanadium compound/organoaluminum compound/silica catalysts, or similar vanadium compound/organometallic compound/inorganic oxide catalysts, on a commercial scale by the various techniques taught in the Monsanto patent have met with varying degrees of success, both from the aspect of the type and quality of the product produced and from the aspect of the commercial acceptability of the technique used to prepare the catalysts.
Although it is believed that it should be possible to prepare satisfactory vanadium compound/organometallic compound/inorganic oxide catalyst compositions by any of the techniques taught by Monsanto, experience has shown that the various techniques which Monsanto indicates to be equivalent are not equivalent in scaled-up processes. For example, in scaled-up processes:
(1) preparation of the catalyst compositions by depositing a vanadium compound/aluminum hydrocarbyloxide/trialkylaluminum formulation on a treated silica support does not lead to the formation of chemically-combined supported catalyst compositions, whereas chemically-combined supported catalyst compositions are prepared when the compositions are prepared by reacting the vanadium compound with the treated support,
(2) preparation of the chemically-combined supported catalyst compositions by Monsanto's vapor deposition technique usually leads to the formation of a black-specked, non-uniform product and is also commercially undesirable because of the technique's requiring the use of vapors that would endanger operators working in the area and therefore necessitate the installation of expensive pollutant-removing equipment,
(3) preparation of the chemically-combined supported catalyst compositions by another of Monsanto's supposedly equivalent techniques, i.e., addition of a solution of the vanadium compound to a dry treated support, also leads to the formation of a non-uniform product, and
(4) preparation of the chemically-combined supported catalyst compositions by the last of Monsanto's supposedly equivalent techniques, i.e., adding a solution of the vanadium compound to a slurry of treated support, is unreliable in the production of a uniform product and, as described in the patent, uses a large amount of hydrocarbon medium which requires accommodation by correspondingly large equipment, high energy costs for evaporation of the medium, and pollution-abatement means.
What is still neeeded is a reproducible, commercially-available process for preparing uniform chemically-combined vanadium compound/organometallic compound/inorganic oxide catalyst compositions--both compositions of the type taught by Monsanto and compositions of other types, e.g., those containing additional components.